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The high limit switch should never trip - if you haven't been keeping the filter clean, call a pro to inspect the heat exchanger right away. (i'm not saying that high limits trip due to cracks - read second post)

If the furnace shuts down just due to a dirty filter, there might be an airflow issue which needs to be addressed and corrected. Fixing the original problem is a lot cheaper than replacing a furnace due to premature failure.

Originally posted by amd The high limit switch should never trip - if you haven't been keeping the filter clean, call a pro to inspect the heat exchanger right away.

If the furnace shuts down just due to a dirty filter, there might be an airflow issue which needs to be addressed and corrected. Fixing the original problem is a lot cheaper than replacing a furnace due to premature failure.

I believe a dirty filter would qualify as a airflow issue.

All high limits that I remember on Yorks are auto reset. There are manual reset rollouts and some counterflow units have manual resets. You need to have someone out to make sure the filter is what caused the problem and not something else.

amd....becareful when you say never, in all actuality a dirty clogged filter will restrict the amount of air being drawn across the HX and increase the temperature inside the furnace. When the increase in temperature exceeds the minimum temperature rating of the High Limit switch, it will trip.

I have rarely seen a high limit switch trip due to a crack in the HX. Either the blower motor had failed, dirty filter, or more commonly the furnace was not properly derated or adjusted to run within it's temperature rise rating. I think you talking about roll-out switches or some auxillary switches which may have a cute little red button on it that can be depressed to reset the switch. But, I think only a trained technician should ever push the pretty little red button.

As for high limit switches, there are three main types:

1) The old honeywell style fan/limit switch,with the bi-metal probe that extends between the HX. No reset, just needs to cool down to get back into operational range. There are a few other types and brands, but the same premises.

2) Newer more common limit switch, which is a metal temperature sensitive diaphram that is extended between the HX. At a certain temperature, the diaphram will expand and open the circuit, when it cools the diaphram will contract to close the circuit. In the case of these the diapram will get week over multiple trips and stay stuck in the open position.

3)Fusible link limit switches are not very common, more in electrical heat products, however, have seen them. this is a diode looking component that is connected in series across the switch, when temperature exceed the rated temperature, the link fails opening the circuit. In this case it must be replaced.

In any case, I have yet to ever see a resettable high limit switch. If the switch is not reseeting by itself, then it needs to be replaced!! This will ensure that in the future when you don't replace the filter, again, the gizmo will keep doing its job by prevent the HX from over heating and failing.

P.S. this is concerning High Limit Switches...... not Roll-Out Switches, or any other Auxillary Switch. So I am presuming we are talking about the High Limit Switch.

I have rarely seen a high limit switch trip due to a crack in the HX. Either the blower motor had failed, dirty filter, or more commonly the furnace was not properly derated or adjusted to run within it's temperature rise rating. I think you talking about roll-out switches or some auxillary switches which may have a cute little red button on it that can be depressed to reset the switch. But, I think only a trained technician should ever push the pretty little red button.

No, you misunderstood.

I suggested getting it looked at simply because overheating due to neglect couldn't have been good for the heat exchanger regardless.

becareful when you say never, in all actuality a dirty clogged filter will restrict the amount of air being drawn across the HX and increase the temperature inside the furnace. When the increase in temperature exceeds the minimum temperature rating of the High Limit switch, it will trip.

Again - sorry, wasn't clear. Dirty and clogged are two different things - if overheating normally occurred due to a little bit of dirt, almost all homeowners would have that problem. (many don't keep it clean)